This invention relates to current mirror circuits and more particularly to an improved transistor circuit suitable for fabrication in integrated circuit form and including additional structure for producing an output current closely matched in magnitude to an input current provided to the current mirror.
Current mirror or current source circuits are well known in the art. Many contemporary current mirror circuits suitable for fabrication in integrated circuit form are considered three terminal circuits comprising an input terminal at which a source of input current is provided; a common terminal at which an operating potential is supplied; and an output terminal to which a load may be connected and at which an output current, substantially equal in magnitude to that of the input current, is provided.
Many of the prior art circuits are comprised of a well known current turn around circuit including a pair of transistors wherein a source of current for establishing the input current is connected to the collector of one of the two transistors. The bases of the two transistors are directly connected to each other and the input current is substantially reproduced at the collector of the second transistor as the output current.
Most, if not all, of the prior art circuits have been concerned with improving the matching between the input and the output current, i.e., improving the ratio of the input current to the output current. However, using lateral PNP transistors, many of these prior art circuits exhibit poor matching, especially when worst case lateral PNP transistor betas (where beta is the forward current gain of the transistor) are considered. Thus, a need exists for providing minimal structure for improving the match between the input and the output current of an integrated current mirror circuit.